Wireless devices commonly include magnetic field transducers in the form of one or more coils wound on a core. Such transducers may be used to sense or extract energy from external magnetic fields, using the current or voltage that is induced in the coils by the fields. Transducers of this sort may alternatively be used as magnetic field generators, by applying a driving current to the coils. One application of such transducers is in wireless position transponders, as described, for example, by Govari in U.S. Patent Application Publication US 2003/0120150 A1, and by Doron et al. in U.S. Pat. No. 6,239,724. The disclosures of both of these publications are incorporated herein by reference.
In some applications, multiple coils may be wound in different directions around the same core, in order to transmit or receive magnetic fields along multiple different axes. For example, PCT patent publication WO 00/38571 A1 and U.S. Pat. No. 6,261,247, to Ishikawa et al., whose disclosures are incorporated herein by reference, describe an anatomical position sensing system using one or more substantially spherical transponders for measuring relative positions and distances. The transponders are capable of receiving and transmitting RF signals, thus communicating between themselves and with a separate CPU. In one embodiment, the transponder is fabricated on a spherical substrate and includes nine coils in three sets of three coils. Each set is orthogonal to the others and comprises three coils: one transmit coil, one receive coil, and one power coupling coil. The coil sets are grouped in this fashion to ensure that at least one coil set is oriented to provide potentially optimum power coupling and signal communication therewith.
Another example of the use of multi-axis magnetic coils in a medical device is described by Casper et al. in U.S. Pat. No. 5,167,626, whose disclosure is also incorporated herein by reference. This patent relates to a medical capsule device actuated by radio-frequency (RF) signal. In one embodiment, three copper wire coils are orthogonally wound around a common ferrite core. The core serves to increase the effective cross-sectional area of the coils. The coil assembly thus provides for the interception of more flux from a magnetic field transmitter and minimizes the dependence of received radio-frequency signal energy on the orientation of the capsule device within the gastrointestinal tract.
There are techniques known in the art for forming or mounting a single-axis magnetic coil on a circuit substrate. For example, U.S. Pat. No. 6,690,255, to Caramela et al., describes a surface-mountable component comprising an elongated core having first and second ends and first and second supports for supporting the core. Each of the supports defines a receptacle for receiving one of the first and second ends of the core. Metallized pads are provided on the supports for electrically connecting and mounting the support to a printed circuit board. At least one wire is wound about a portion of the core and has its ends electrically connected to the metallized pads of the supports. Components of this sort are available from Coilcraft Inc. (Cary, Ill.).